Magneto ignition system for internal combustion engines

ABSTRACT

To prevent operation of the engine in reverse direction of rotation, an auxiliary winding on the magneto is connected with the pulse source which provides ignition trigger pulses by an unsymmetrical conduction network, including diodes, which prevent application of trigger pulses from the pulse source to a control switch connecting an energy storage capacitor to discharge through the ignition coil, thus providing an ignition pulse, unless both the pulse source and the auxiliary winding provide, simultaneously, instantaneous output voltages of a predetermined polarity which is in direction to trigger the pulse source. Preferably, the auxiliary winding is formed as a tapped portion of the main magneto winding.

[4 1 Feb. 11, 1975 1 MAGNETG IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGlNES [75] Inventor: Peter Schmaldienst,Nurnberg,

Germany [73] Assignee: Robert Bosch Gmbll, Stuttgart,

Germany 22 Filed: .lulyll,1973

211 App1.No.:378,l95

[30] Foreign Application Priority Data 3,791,363 2/1974 Schmaldienst et al. 123/148 E 3,795,235 3/1974 Donohue et .al. 123/148 S X Primary ExaminerCharles .1. Myhre Assistant Examiner-Tony Argenbright Attorney, Agent, or FirmFlynn & Frishauf [57] ABSTRACT To prevent operation of the engine in reverse direction of rotation, an auxiliary winding on the magneto is connected with the pulse source which provides ignition trigger pulses by an unsymmetrical conduction network, including diodes, which prevent application of trigger pulses from the pulse source to a control switch connecting an energy storage capacitor to discharge through the ignition coil, thus providing an ignition pulse, unless both the pulse source and the auxiliary winding provide, simultaneously, instantaneous output voltages of a predetermined polarity which is in direction to trigger the pulse source. Preferably, the auxiliary winding is formed as a tapped portion of the main magneto winding.

6 Claims, 3 Drawing Figures MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES The present invention relates to a magneto ignition system for internal combustion engines in which an energy storage device, preferably a capacitor, is supplied from a magento generator which supplies alternating current energy, and a discharge trigger element, for example a thyristor is connected in the circuit to provide the ignition discharge pulse. More specifically, when the direction of rotation of the engine is proper, the ignition pulse will be delivered at the proper timing instant for the internal combustion engine; when the direction of rotation of the engine is reversed, for example upon kickback of the engine, ignition pulses are inhibited.

Ignition systems of the general type have previously been provided with reverse-direction safety devices by extensive electronic circuits utilizing a plurality of component, or by unsymmetrical magnetization of the field of the magneto generator. Unsymmetrical magnetization impairs efficient utilization of the magneto generator, particularly when the magneto is used to supply current not only to the ignition system but further to other loads, typically the lighting system of the vehicle.

It has been found that simplified solutions which prevent reverse rotation of the internal combustion engines, such as magnetic pulse sources which are flattened on one side are not always reliable in operation.

It is an object of the present invention to provide a simple electrical circuit with few elements and components which, additionally, are readily available and inexpensive, while providing for reliable insurance against reverse rotation of the engine.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the magneto is formed with an auxiliary winding, which is connected to a pulse source by an unsymmetrical circuit which includes diodes, which are so connected, logically, that only when the instantaneous voltage from the auxiliary winding and the pulse source, simultaneously, has a single predetermined polarity, a trigger pulse will be delivered by the unsymmetrical circuit. It is thus possible to construct the circuit simply of diodes, and to provide a tap point on the magneto winding to obtain the auxiliary winding portion thereof.

In a preferred form of the invention, the pulse source has one terminal connected to one end of the winding of the magneto generator, the other terminal to a diode which is connected in conductive direction to the gate or trigger electrode of a thyristor, the main current path of which is connected to discharge a storage capacitor to provide the ignition pulse. A further diode is connected between the auxiliary winding, preferably a tap point of the main winding of the magneto and the other terminal of the pulse source, likewise poled in conductive direction when the voltage is proper to trigger the thyristor.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a general schematic block diagram of the system of the present invention;

FIG. 2 is a graph of voltages versus time when the engine is running in its proper, forward direction and FIG. 3 is a similar graph of voltages versus time when the engine is operating in reverse direction, for example by being driven, or upon kickback of the engine.

Magneto generator 10 (FIG. 1)) is illustrated to supply a single cylinder internal combustion engine. It has a field 11, secured with its hub (not shown) to a shaft of the internal combustion engine, and cooperating with an armature 12, likewise secured to the internal combustion engine (not shown). Field 11 forms a magnetic system including a group of permanent magnets 13, symmetrically located at the circumference of the field and magnetized with alternating polarity. The armature 12 includes an armature winding 14, with end terminals 14a, 14b. End terminal 14a is connected over diode 15 with a storage capacitor 16, the other terminal of which is connected to the chassis of the vehicle. The other terminal 14b of winding 14 is likewise connected to chassis. The discharge circuit for the capacitor 16 is in parallel thereto and includes the primary 17a of an ignition coil 17, and a series connected thyristor 18, the other terminal of which is connected to chassis. The ignition coil 17 has its secondary 1712 connected to the primary 17a, and the high terminal thereof to a spark plug 19, shown only schematically. The thyristor 18 has a control or gate electrode 18a. It is triggered from a pulse source 20, one terminal 200 is connected to chassis, the other terminal 20b being connected through a diode 21, poled in conductive direction with the gate electrode 18a of the thyristor 18, that is, so poled that a trigger pulse from pulse source 20 when applied to gate electrode 18a will have the proper polarity to trigger the gate electrode.

The ignition system must be so arranged that the ignition pulse resulting in a spark at spark plug 19 is inhibited when the engine operates in the reverse direction. The circuit of FIG. 1 includes a further diode 22, connected to terminal 20b of pulse source 20 on the one hand, and with a tap point 23 of the main winding or armature 14 of the magneto. The end 14b of the magneto armature 14 and the terminal 200 of pulse source 20 are cross connected by the chassis of the vehicle. Diode 22 and the tap point 23 of the winding 14, and the cross connection thus form a further closed network. The diode 22 is poled in conductive direction. The output voltage of the auxiliary winding formed of portion 14' of the armature 14 is so selected that an alternating voltage is induced by the field ll of magneto 10 in the auxiliary winding such that its amplitude is slightly higher than the amplitude of the pulses derived from pulse source 20.

Operation, with reference to FIGS. 2 and 3: If the direction of rotation of the engine is proper, or forward, an alternating voltage will be induced in the armature 14 of magneto 10 which varies between +200V to 2000 V. During the negative half waves, diode 15 is blocked. Capacitor 16 will thus charge only during positive half waves, through a voltage Uc. The tap 23 of winding 14 will likewise have an alternating voltage arising thereat which is shown in FIGS. 2 and 3 as Ug. This is a counter voltage. The pulse source 20 provides control pulses Ust. During the first positive half wave of voltage Ug, no control pulse will be generated in pulse source 20. The anode of diode 22 is thus as chassis potential, and the positive half wave of voltage Ug is blocked. At the second half wave from pulse source 20, which is negative, no control pulse will be generated in pulse source 20. Diode 212 has its cathode at negative potential and is conductive, and current will flow through pulse source in diode 22 which is determined by the inherent resistance of pulse source 20, the resistance of the winding portion 14 between taps 23 and terminal 14b of the charge winding and the inherent resistance of diode 22. Voltage drop across the pulse source 20 is negative with respect to chassis voltage, and thus will not be effective at the control electrode 18a of thyristor 18.

Pulse source 20 provides a control pulse Ust at the proper ignition instant by a magnetic element passing along the armature 20 of the pulse generator. This control pulse Ust will occur during the third positive half wave of the counter voltage Ug from the magneto. The control pulse Ust is a rapid sequence of a positive and negative voltage peak. The higher amplitude of the positive voltage half wave Ug from the magneto with respect to the positive voltage peak of the control pulse Ust causes diode 22 to remain blocked, so that the positive voltage peak of the control pulse Ust from pulse source 20 can be transferred over diode 21 to the control electrode 18a of thyristor 18. Thyristor 18 will switch to become conductive, energy stored in capacitor 16 will discharge through primary 17a of the ignition coil and the now conductive thyristor 18, causing generation of an ignition pulse in the secondary and a spark at spark plug 19. At the next positive voltage half wave of generator 14, capacitor 16 will recharge. The described sequence will cyclically repeat with each full revolution of armature 11 of the magneto.

Let it be assumed that the engine operates in reverse direction, so that the armature 11 will operate in reverse direction as well, for example upon kickback of the engine. The voltage values, in the same positions of the field, will reverse by 180. The first half wave of the voltage Ug is now negative. Diode 22 becomes conductive and current will flow over pulse source 20 and diode 22 as before. The second positive half wave of voltage Ug, however, will be ineffective with respect to the trigger circuit (capacitor 16 will become charged), since diode 22 will block. The third voltage half wave is again negative, and diode 22 becomes conductive. During the third half wave, a pulse Ust will be derived from pulse source 20. The negative portion of the pulse is short circuited over diode 22 and the winding portion 14 of the armature winding 14 (assumed to have a relatively low resistance). The pulse source 20 has a relatively high inherent resistance, and the positive voltage peak of the control pulse Ust will rapidly collapse, so that thyristor 18 remains blocked. Discharge of the storage capacitor 16, and thus an ignition pulse to spark plug 19 is prevented.

The negative voltage half waves from the winding portion 14' of armature 14 may load the pulse source 20 to cause undesired heating thereof. Under such conditions, a further diode can be provided, poled as shown (anode at chassis and cathode at tap 23). Since this further diode 25 is not strictly necessary, the connections are shown in dash lines.

The present invention has been described in connection with an operating example, although many modifications and changes can be made. For example, the voltage Ug can be obtained from a separate auxiliary winding, not merely from an auxiliary winding portion of the main winding 14. Such a separate auxiliary winding can be wound on the armature on which the main winding 14 is placed as well as on a separate, auxiliary armature, in magnetic circuit with the field 11, or with a portion thereof, or a separate field 11. The control system can be used for multicylinder engines, in which each cylinder has its own discharge circuit for the ignition system and a pulse source to control a discharge controlling thyristor. The various pulse sources, which may have a single magnet 24 and a plurality of pulse windings 20, or suitably switched outputs, can then be connected over a diode each to the tap point 23, or to a separate auxiliary winding. These diodes, additionally, decouple the control systems of the various cylinders from each other.

The principle of the present invention can be used to operate the internal combustion engine in two selected directions of rotation, with minor modifications of the circuit, in such a manner that in each instant the reverse direction of rotation, as selected, will be suppressed. By means of a multicontact transfer switch (which can be also a suitable solid state circuit) a multigate thyristor (in which one gate is responsive to positive pulses and the other to negative pulses) is triggered upon coincidence of the negative half waves of the voltage Ug and the voltage Ust, as seen in FIG. 3. To derive this voltage, a further diode is connected in the circuit which carries the short circuit current explained in connection with FIG. 3, by suitable switching of the multiposition switch, to block the short circuit current and, rather, transfer the current to the additional, negatively responding gate electrode of the thyristor.

I claim:

1. Magneto ignition system for internal combustion engines having a spark plug, comprising a magneto generator (10) having a main winding an energy storage element (16) supplied by the generator; controlled switching means (18) having a control terminal (18a) to permit application of stored energy in a storage element to the spark plug (19);

and a pulse source (20) having one terminal (20b) connected to the control terminal (18b) to trigger the controlled switch (18) into conduction and thus apply stored energy to the spark plug, wherein the improvement comprises an auxiliary winding (14') on the magneto generator and unsymmetrical conduction means (21, 22) conmeeting a. the auxiliary winding (14) of the magneto to the pulse source and b. the pulse source (20) to the control terminal said unsymmetrical conduction means being logically connected to the auxiliary winding (14') and to the pulse source (20) to become conductive only if both the pulse source and the auxiliary winding provide, simultaneously, an instantaneous output voltage of predetermined polarity; wherein the auxiliary winding and the unsymmetrical conduction means form a reverse rotation inhibiting circuit comprising a cross connection between one terminal (14b) of the auxiliary winding and one terminal (20a) of the pulse source (20);

a connecting diode connecting the other terminal of the auxiliary winding (23) and the other terminal (20b) of the pulse source (20), said diode being poled in conductive direction to transfer generated voltage pulses in said auxiliary winding to the pulse source (20);

and a coupling diode (21) poled in conductive direction to connect the other terminal (20b) of the pulse source with the control terminal (18a) of the controlled switching means (18) to provide trigger pulses to the controlled switch only when the voltages from the pulse source and the auxiliary winding are of proper polarity to energize the controlled switching means.

2. System according to claim 1 wherein the cross connection is a connection to chassis of the internal combustion engine.

3. System according to claim 1 further comprising a bridging diode (25) connected in shunt with the auxiliary winding (14') of the magneto generator and poled to bypass transfer of voltages from the magneto to the pulse source when there are no counteracting voltages being generated in the pulse source.

4. System according to claim 3 wherein the bridging diode (25) has its anode connected to said cross connection and its cathode connected to the auxiliary winding (23).

5. System according to claim 1 wherein the auxiliary winding (14) is a portion of the main winding (14) of the magneto generator (10), the other terminal of said winding (14b) being defined by an end terminal (14b) of the main winding and said one terminal (23) being defined by a tap (23) on the main winding (14), the main winding having a first terminal (14a) connected to the energy storage element (16).

6. System according to claim 5 wherein the energy storage element comprises a capacitor (16). 

1. Magneto ignition system for internal combustion engines having a spark plug, comprising a magneto generator (10) having a main winding (14); an energy storage element (16) supplied by the generator; controlled switching means (18) having a control terminal (18a) to permit application of stored energy in a storage element to the spark plug (19); and a pulse source (20) having one terminal (20b) connected to the control terminal (18b) to trigger the controlled switch (18) into conduction and thus apply stored energy to the spark plug, wherein the improvement comprises an auxiliary winding (14'') on the magneto generator (10); and unsymmetrical conduction means (21, 22) connecting a. the auxiliary winding (14'') of the magneto to the pulse source and b. the pulse source (20) to the control terminal (18a), said unsymmetrical conduction means being logically connected to the auxiliary winding (14'') and to the pulse source (20) to become conductive only if both the pulse source and the auxiliary winding provide, simultaneously, an instantaneous output voltage of predetermined polarity; wherein the auxiliary winding and the unsymmetrical conduction means form a reverse rotation inhibiting circuit comprising a cross connection between one terminal (14b) of the auxiliary winding and one terminal (20a) of the pulse source (20); a connecting diode connecting the other terminal of the auxiliary winding (23) and the other terminal (20b) of the pulse source (20), said diode being poled in conductive direction to transfer generated voltage pulses in said auxiliary winding to the pulse source (20); and a coupling diode (21) poled in conductive direction to connect the other terminal (20b) of the pulse source with the control terminal (18a) of the controlled switching means (18) to provide trigger pulses to the controlled switch only when the voltages from the pulse source and the auxiliary winding are of proper polarity to energize the controlled switching means.
 2. System according to claim 1 wherein the cross connection is a connection to chassis of the internal combustion engine.
 3. System according to claim 1 further comprising a bridging diode (25) connected in shunt with the auxiliary winding (14'') of the magneto generator (10) and poled to bypass transfer of voltages from the magneto to the pulse source when there are no counteracting voltages being generated in the pulse source.
 4. System acCording to claim 3 wherein the bridging diode (25) has its anode connected to said cross connection and its cathode connected to the auxiliary winding (23).
 5. System according to claim 1 wherein the auxiliary winding (14'') is a portion of the main winding (14) of the magneto generator (10), the other terminal of said winding (14b) being defined by an end terminal (14b) of the main winding and said one terminal (23) being defined by a tap (23) on the main winding (14), the main winding having a first terminal (14a) connected to the energy storage element (16).
 6. System according to claim 5 wherein the energy storage element comprises a capacitor (16). 